US8135295B2 - Image forming apparatus with a developing device utilizing an alternating bias voltage - Google Patents

Image forming apparatus with a developing device utilizing an alternating bias voltage Download PDF

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US8135295B2
US8135295B2 US12/488,764 US48876409A US8135295B2 US 8135295 B2 US8135295 B2 US 8135295B2 US 48876409 A US48876409 A US 48876409A US 8135295 B2 US8135295 B2 US 8135295B2
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period
bearing member
alternating voltage
peak
electrostatic latent
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US20090317143A1 (en
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Toshimasa Hamada
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Sharp Corp
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Sharp Corp
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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G15/00—Apparatus for electrographic processes using a charge pattern
    • G03G15/06—Apparatus for electrographic processes using a charge pattern for developing
    • G03G15/08—Apparatus for electrographic processes using a charge pattern for developing using a solid developer, e.g. powder developer
    • G03G15/09—Apparatus for electrographic processes using a charge pattern for developing using a solid developer, e.g. powder developer using magnetic brush
    • G03G15/0907—Apparatus for electrographic processes using a charge pattern for developing using a solid developer, e.g. powder developer using magnetic brush with bias voltage
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G2215/00—Apparatus for electrophotographic processes
    • G03G2215/06—Developing structures, details
    • G03G2215/0602—Developer
    • G03G2215/0604—Developer solid type
    • G03G2215/0607—Developer solid type two-component
    • G03G2215/0609—Developer solid type two-component magnetic brush

Definitions

  • the present invention relates to an image forming apparatus for applying an alternating voltage superimposed on a direct current voltage to a developer bearing member to thereby develop an electrostatic latent image formed on an electrostatic latent image bearing member with a toner.
  • an electrophotographic image forming apparatus a development method has been employed in which a surface of an electrostatic latent image bearing member (for example, a photoreceptor) is charged and an image is exposed to the charged region to from an electrostatic latent image, and the electrostatic latent image is developed so as to be made visible (developing).
  • an electrostatic latent image bearing member for example, a photoreceptor
  • a development method As such a development method, a development method has been commonly used in which, using one-component developer containing a toner or two-component developer containing a carrier and a toner, by frictionally charging the toner so that the toner is attracted with an electrostatic force of an electrostatic latent image on the surface of the electrostatic latent image bearing member, the electrostatic latent image is developed to thereby form a toner image.
  • a method in which a magnetic brush by carrier is formed on a developer bearing member (for example, a developing roller) in a developing device, and an electrostatic latent image is developed while applying a bias voltage between the developer bearing member and an electrostatic latent image bearing member.
  • a developer bearing member for example, a developing roller
  • one-component or two-component developer there is a case where development is performed using a toner that is charged with a polarity opposite to a surface potential of the charged electrostatic latent image bearing member, or a case where reversal development is performed using a toner that is charged with a polarity the same as the surface potential of the charged electrostatic latent image bearing member.
  • an electrostatic latent image that is formed on the electrostatic latent image bearing member is developed with the toner by applying an oscillating bias voltage between the developer bearing member and the electrostatic latent image bearing member.
  • a development-side electrical potential i.e., a for-development electrical potential
  • an opposite development-side electrical potential i.e., an against-development electrical potential
  • a rectangular wave is commonly used whose ratio (duty ratio) of the application time during which the development-side electrical potential is applied to the application time of a cycle during which the development-side electrical potential and the opposite development-side electrical potential are applied is 50%.
  • the charge amount of the toner is increased to obtain smooth image quality with little roughness.
  • the electrostatic force between a carrier and a toner is in proportion to the square of the charge amount, thus, when the charge amount of the toner is increased, a rate that the carrier separates from the toner decreases. Accordingly, the utilization efficiency of the toner consequently deteriorates and the image density is reduced.
  • an oscillation amplitude voltage Vpp peak-to-peak voltage
  • An object of the invention is to provide an image forming apparatus capable of realizing improvement of an image density by improving dot reproducibility and reducing fog as well.
  • the invention provides an image forming apparatus comprising:
  • a developing device that has a developer bearing member and develops the electrostatic latent image formed on the electrostatic latent image bearing member with one by applying an alternating voltage superimposed on a DC voltage to the developer bearing member
  • the alternating voltage to be applied having an alternating voltage waveform in which a development-side potential to move toner from the developer bearing member to the electrostatic latent image bearing member and an opposite development-side potential to move toner from the electrostatic latent image bearing member to the developer bearing member alternate with each other, and
  • a first period during which a first peak-to-peak voltage is applied and a second period during which a second peak-to-peak voltage lower than the first peak-to-peak voltage is applied being alternately repeated and a frequency of the alternating voltage in the second period being lower than a frequency of the alternating voltage in the first period.
  • an image forming apparatus comprises an electrostatic latent image bearing member on which an electrostatic latent image is to be formed, and a developing device that has a developer bearing member and develops the electrostatic latent image formed on the electrostatic latent image bearing member with toner by applying an alternating voltage superimposed on a DC voltage to the developer bearing member.
  • the alternating voltage is applied so that a first period during which a first peak-to-peak voltage is applied and a second period during which a second peak-to-peak voltage lower than the first peak-to-peak voltage is applied are alternately repeated.
  • a frequency of the alternating voltage in the second period is lower than a frequency of the alternating voltage in the first period.
  • a potential that is applied at an end of the first period is a development-side potential in the alternating voltage.
  • a potential that is applied at an end of the first period is a development-side potential so that a toner that has once reached a latent image on the electrostatic latent image bearing member will not be peeled off, resulting that the image density is increased and dot reproducibility is also enhanced.
  • the potential that is applied at an end of the first period is the opposite development-side potential, the image density is decreased and dot reproducibility is deteriorated.
  • a periodic number included in the first period is 2 or 3 in the alternating voltage.
  • a periodic number included in the first period is 2 or 3. Since fog is increased when the periodic number included in the first period is 1, the number is preferably 2 or more, and since dot reproducibility is lowered in the case of being 4 or more, the number is preferably 2 or 3.
  • a periodic number included in the second period is 1 in the alternating voltage.
  • the periodic number included in the second period is 1.
  • the time for applying the opposite development-side potential is made longer so that fog can be suppressed.
  • Vpp( 1 ) denotes a peak-to-peak voltage in the first period
  • Vpp( 2 ) denotes a peak-to-peak voltage in the second period.
  • Vpp( 1 ) denotes a peak-to-peak voltage in the first period
  • Vpp( 2 ) denotes a peak-to-peak voltage in the second period
  • Vpp( 2 ) As a value of Vpp( 2 ) becomes smaller, a toner is easily moved to the latent image and dot reproducibility is therefore improved, however, fog is deteriorated when the value becomes too small, and therefore, the value preferably falls within the range.
  • T 1 denotes a length of the first period
  • T 2 denotes a length of the second period
  • T 1 denotes a length of the first period
  • T 2 denotes a length of the second period
  • T 2 /T 1 When T 2 /T 1 is smaller than 0.7, fog is deteriorated, and when T 2 /T 1 is larger than 2.5, dot reproducibility is lowered.
  • the peak-to-peak voltage in the first period Vpp( 1 ) satisfies the following expression in the alternating voltage: 1 kV ⁇ Vpp(1) ⁇ 3 kV.
  • the peak-to-peak voltage in the first period Vpp( 1 ) satisfies 1 kV ⁇ Vpp( 1 ) ⁇ 3 kV.
  • Vpp( 1 ) In the case where Vpp( 1 ) is lower than 1 kV, the image density is insufficient. In the case where Vpp( 1 ) is higher than 3 kV, a spot-like white void is easily generated due to a leak current between the electrostatic latent image bearing member and the developer bearing member, thus being difficult to use.
  • t 1 and t 2 are differentiated at least in the first period of the alternating voltage, where ti denotes a time during which the development-side potential is applied and t 2 denotes a time during which the opposite development-side potential is applied.
  • t 1 and t 2 are differentiated at least in the first period, where t 1 denotes a time during which the development-side potential is applied and t 2 denotes a time during which the opposite development-side potential is applied.
  • t 1 >t 2 it is possible to further suppress fog
  • t 1 ⁇ t 2 it is possible to enhance dot reproducibility.
  • t 1 and t 2 satisfy the following expression at least in the first period of alternating voltage: 0.35 ⁇ t 1/( t 1 +t 2) ⁇ 0.70.
  • t 1 and t 2 satisfy 0.35 ⁇ t 1 /(t 1 +t 2 ) ⁇ 0.70 at least in the first period.
  • a two-component developer including a toner and a carrier is used as a developer.
  • the toner in the case where a two-component developer including a toner and a carrier is used as the developer, the toner is likely to separate from carrier and the utilization efficiency of toner is enhanced. Accordingly, such an effect is achieved that unevenness in magnetic chains is less likely to be conspicuous and it is suitable for development using two-component developer.
  • FIG. 1 is a vertical cross sectional view schematically showing an overview of an entire configuration of an image forming apparatus according to a first embodiment
  • FIG. 2 is a side view showing a schematic configuration of a developing device in each of image forming stations shown in FIG. 1 ;
  • FIG. 3 is a view showing a developing bias voltage waveform in the first embodiment
  • FIG. 4 is a view showing a developing bias voltage waveform in a case where a final potential is an opposite development-side potential
  • FIG. 5 is a graph showing results of comparing image densities in Example and Comparative examples
  • FIG. 6 is a graph showing results of comparing dot reproducibility in Example and Comparative examples
  • FIG. 7 is a graph showing results of comparing fog in Example and Comparative examples
  • FIG. 8 is a view showing a developing bias voltage waveform in a second embodiment
  • FIG. 9 is a view showing a developing bias voltage waveform in a conventional technology
  • FIG. 10 is a view showing a developing bias voltage waveform in a conventional technology.
  • FIG. 11 is a view showing a developing bias voltage waveform in a conventional technology.
  • FIG. 1 is a vertical cross sectional view schematically showing an overview of an entire configuration of an image forming apparatus 100 according to a first embodiment. Note that, for simplicity, FIG. 1 shows an example of the image forming apparatus 100 of this embodiment mainly with principal components, which is not limited to a configuration of an image forming apparatus that performs a development method according to the invention.
  • the image forming apparatus 100 is a tandem type color image forming apparatus capable of forming a color image, which includes a plurality of photoreceptors 51 serving as an electrostatic latent image bearing member (in this embodiment, four photoreceptors for yellow images, magenta images, cyan images, and black images).
  • the image forming apparatus 100 has a printer function of forming a color image or a monochrome image on a sheet P serving as a transfer receiving member (recording medium) based on image data transmitted from various kinds of information processing terminal apparatus (not shown) such as a PC (Personal Computer) connected through a network (not shown) or image data read by a document reading apparatus (not shown) such as a scanner As shown in FIG.
  • the image forming apparatus 100 includes image forming station section 50 ( 50 Y, 50 M, 50 C, and 50 B) having a function of forming an image on the sheet P, a fixing device 40 having a function of fixing a toner image formed on the recording medium P at the image forming station section 50 , and a transport section 30 having a function of transporting the recording medium P from a feed tray 60 on which the recording medium P is placed to the image forming station section 50 and the fixing device 40 .
  • image forming station section 50 50 Y, 50 M, 50 C, and 50 B
  • a fixing device 40 having a function of fixing a toner image formed on the recording medium P at the image forming station section 50
  • a transport section 30 having a function of transporting the recording medium P from a feed tray 60 on which the recording medium P is placed to the image forming station section 50 and the fixing device 40 .
  • the image forming station section 50 is configured with four image forming stations 50 Y, 50 M, 50 C, and 50 B for yellow images, magenta images, cyan images, and black images, respectively.
  • the yellow image forming station 50 Y, the magenta image forming station 50 M, the cyan image forming station 50 C, and the black image forming station 50 B are disposed in this order from the side of the feed tray 60 between the feed tray 60 and the fixing device 40
  • the image forming stations 50 Y, 50 M, 50 C, and 50 B for the respective colors have substantially the same structure, and form yellow, magenta, cyan, and black images according to image data corresponding to the respective colors so that the images are eventually transferred onto the sheet P serving as the transfer receiving member (recording medium).
  • the image forming station section 50 of this embodiment has a configuration to form images in four colors of yellow, magenta, cyan, and black, but may have a configuration to form images in six colors additionally including, for example, light cyan (LC) and light magenta (Lm) that have the same color hues as cyan and magenta and have a lower density, without limitation to the four colors.
  • LC light cyan
  • Lm light magenta
  • FIG. 1 the components of the respective image forming station section are shown with alphanumeric references on the yellow image forming station 50 Y as a representative, and the alphanumeric references of the components of the other image forming stations 50 N, 50 C, and 50 B are omitted.
  • the image forming stations 50 Y, 50 M, 50 C, and 50 B respectively includes the photoreceptor 51 serving as a latent image bearing member on which an electrostatic latent image is formed, and a charging device 52 , an exposure unit 53 , a developing device 1 , a transfer device 55 , and a cleaning unit 56 are disposed in the circumferential direction around the photoreceptor 51 .
  • the photoreceptor 51 is in the shape of a substantially cylindrical drum on the surface of which a photosensitive material such as an OPC (Organic Photoconductor) is provided, and is disposed below the exposure unit 53 and controlled so as to be rotationally driven in a predetermined direction (in the direction shown with an arrow F in the figure) by a driving section and a control section.
  • a photosensitive material such as an OPC (Organic Photoconductor)
  • the charging device 52 is a charging section that uniformly charges the surface of the photoreceptor 51 to a predetermined potential, and is disposed above the photoreceptor 51 so as to be close to a peripheral surface thereof.
  • a roller system charging roller in a contact type is used, but a charging device of a charger type, a brush type, an ion emission-charging type, a magnetic brush-charging type or the like may be used as a substitution therefor.
  • the exposure unit 53 has a function of exposing the surface of the photoreceptor 51 that is charged with the charging device 52 by irradiating it with laser light based on image data outputted from an image processing section (not shown) to thereby write and form an electrostatic latent image according to the image data on the surface.
  • the exposure unit 53 forms an electrostatic latent image in a corresponding color when image data that corresponds to yellow, magenta, cyan, or black is inputted respectively according to the image forming stations 50 Y, 50 M, 50 C, or 50 B.
  • a laser scanning unit including a laser irradiation section and a reflection mirror or a write device (for example, a write head) in which light emitting elements such as ELs and LEDs are arranged in an array is usable.
  • the developing device 1 has a developing roller 3 serving as a developer bearing member that bears developer.
  • the developing roller 3 is configured so that developer is transported to a development region in which toner can move to the photoreceptor 51 .
  • the developing device 1 uses two-component developer including toner and carrier, and forms a toner image (visible image) by performing reversal development with the toner of an electrostatic latent image that has been formed on the surface of the photoreceptor 51 by the exposure unit 53 .
  • the developing device 1 contains yellow, magenta, cyan, or lack developer according to image formation of the respective image forming stations 50 Y, 50 M, 50 C, and 50 B.
  • the developer includes toner that is charged with a polarity the same as the surface potential that is charged to the photoreceptor 51 . Note that, the polarity of the surface potential that is charged to the photoreceptor 51 and the charged polarity of the toner used are both negative in this example.
  • the transfer device 55 transfers a toner image on the photoreceptor 51 to the transfer receiving member P that is transported by a transport belt 33 , and is provided with a transfer roller to which a bias voltage that has a polarity (positive in this example) opposite to the charged polarity of the toner is applied.
  • the cleaning unit 56 removes and collects the toner remaining on the peripheral surface of the photoreceptor 51 after the development and image transfer to the sheet P serving as the transfer receiving member.
  • the cleaning unit 56 is disposed substantially horizontally in the side of the photoreceptor 51 at a position substantially facing the developing device 1 across the photoreceptor 51 (in the left side in FIG. 1 ).
  • the transport section 30 includes a drive roller 31 , a driven roller 32 , and the transport belt 33 , and transports the transfer receiving member P to which toner images in the respective colors are transferred in the image forming stations 50 Y, 50 M, 50 C, and 50 B.
  • the transport section 30 is configured so that the endless transport belt 33 is routed around the drive roller 31 and the driven roller 32 , and transports the sheet P serving as the transfer receiving member (recording medium) that is fed from the feed tray 60 to each of the image forming stations 50 Y, 50 , 50 C, and 50 B sequentially.
  • the fixing device 40 includes a heat roller 41 and a pressure roller 42 , and by transporting the transfer receiving member P to a nip portion, applies heat and pressure to the toner image transferred to the sheet P to fix on the sheet P.
  • the image forming apparatus 100 of this embodiment includes a bias voltage applying section that applies an oscillating bias voltage to the developing roller 3 so that a potential difference between the developing roller 3 and the photoreceptor 51 is changed continuously and periodically.
  • the oscillating bias voltage is an alternating voltage in which a development-side electrical potential that can apply a force to the toner to be charged in the direction from the developing roller 3 to the photoreceptor 51 and an opposite development-side electrical potential that can apply a force to the toner to be charged in the direction from the photoreceptor 51 to the developing roller 3 alternate with each other.
  • the application of the oscillating bias voltage will be described in detail later.
  • the toner images on the respective photoreceptors 51 are successively transferred to the sheet P with the action of a transfer electric field of the transfer rollers of the transfer device 55 that is disposed below the facing positions thorough the transport belt 33 .
  • the sheet P serving as the transfer receiving member on which the toner image is transferred in such a manner is subjected to a fixing process of the toner image at the fixing device 40 and thereafter is discharged to a discharge tray (not shown).
  • FIG. 2 is a schematic view showing an outline of the structure of the developing device 1 in the respective image forming stations shown in FIG. 1 .
  • FIG. 2 shows an example in which the primary components of the developing device 1 are mainly described simplistically, without any limitation to the structure of the developing device implementing the developing method according to the invention.
  • the developing device 1 includes, in addition to the above-described developing roller 3 , a regulation blade 6 serving as a regulation member that regulates the layer thickness of developer on the developing roller 3 , a pair of agitating/conveying screws 4 and 5 serving as agitating/conveying members that convey the developer to the developing roller 3 and agitate the developers and a developing tank 2 that contains two-component developer including toner and carrier.
  • a regulation blade 6 serving as a regulation member that regulates the layer thickness of developer on the developing roller 3
  • a pair of agitating/conveying screws 4 and 5 serving as agitating/conveying members that convey the developer to the developing roller 3 and agitate the developers
  • a developing tank 2 that contains two-component developer including toner and carrier.
  • the pair of agitating/conveying screws 4 and 5 are disposed so as to be substantially in parallel to each other.
  • a partition 7 is provided between the agitating/conveying screws 4 and 5 so as to partition the developing tank 2 therebetween except for both end sides in the axial line direction.
  • toner in the developer contained in the developing tank 2 is agitated with carrier by an agitation operation of the agitating/conveying screws 4 and 5 disposed in the developing tank 2 so as to be frictionally charged.
  • an opening section for development Q is provided at a position in the development unit 2 that faces the photoreceptor 51 , and the developing roller 3 is disposed in the developing tank 2 in a state where a part of which is exposed from the opening section for development Q of the development unit 2 with a development gap (about 0.3 to 1.0 mm) between the photoreceptor 51 .
  • the developing roller 3 has a magnet roller 8 in which a plurality of magnetic pole members are arranged along the circumferential direction, and a nonmagnetic development sleeve 9 formed with aluminum alloy and brass in a substantially cylindrical shape that is fitted in the magnet roller 8 so as to rotate freely in a fixed direction (in the direction shown with arrow G in FIG. 2 ), and is configured so that the development sleeve 9 is rotationally driven in a predetermined direction (in the direction shown with arrow G in FIG. 2 ) by a control section and driving section (not shown).
  • the developer is two-component developer including toner and carrier that is composed of a magnetic substance.
  • the developer is attracted to the surface of the development sleeve 9 by the magnetic force of the magnet, and is conveyed on the development sleeve 9 along the rotational direction G of the development sleeve 9 .
  • the carrier is attracted to the surface of the development sleeve 9 by the magnetic force of the magnet roller 8 so as to form a magnetic brush, and the toner is attached to the carrier by Coulomb force due to the frictional charge.
  • a tip portion of the regulation blade 6 is disposed so as to face the development sleeve 9 in the upstream side of the rotational direction G of the development sleeve 9 in the opening section for development Q.
  • the regulation blade 6 is configured so that the layer thickness of developer formed on the surface of the developing roller 3 is regulated.
  • the developing device forms a toner image by supplying a constant amount of developer to a position that faces the photoreceptor 51 , attracting the toner in the developer supplied to the facing position with the electrostatic force of an electrostatic latent image formed on the surface of the photoreceptor 51 , and developing the electrostatic latent image. Also, in the developing device 1 , the carrier and the toner that has not been used for development of the developer supplied to the facing position returns into the developing tank 2 with the rotation of the development sleeve 9 .
  • a toner whose shape factor SF- 1 is in a range of 100 to 160 and toner whose shape factor SF- 2 is in a range of 100 to 150 are usable, and more preferably, the SF- 1 is 110 to 150 and the SF- 2 is 110 to 140.
  • the toner shape factor SF- 1 represents a degree of a roundness of toner particles and the shape factor SF- 2 represents a degree of unevenness of the surface of toner particles.
  • the shape factor is a value obtained by randomly sampling 100 toner images magnified 500 times that have been shot with the use of, for example, FE-SEM (S-800) manufactured by Hitachi, Ltd. and analyzing image information thereof with an image analysis apparatus (Luzex III) manufactured by Nireco Corporation, for example.
  • toner has a shape similar to a spherical shape, and therefore, there is a case where the toner slips on an endless conveyance belt to cause distortion of a transfer image when the toner is transferred from the photoreceptor to the endless conveyance belt.
  • toner is greatly deformed and a projected portion on the toner surface is separated from the toner surface by stirring to be fine powders which cause toner dispersion or adhere to the carrier surface or the development sleeve surfacer resulting in inhibition of sufficient friction charge with the toner in some cases.
  • the toner surface has high smoothness, and there is a case where the toner slips on the endless conveyance belt to cause distortion of the transfer image similarly to the case of SF- 1 ⁇ 110.
  • toner surface has large unevenness and there is a case where a variation is generated in a charge amount of individual toner and the image density is not stabilized to cause fog.
  • a toner weight in an image area having 100% image area rate of a transfer image falls within a range of 0.20 to 0.50 mg/cm 2
  • the toner weight in the image area having 100% image area rate of the transfer image is preferably adjusted within a range of 0.60 to 1.5 mg/cm 2 .
  • the toner to be used in the invention is able to be prepared by a known manufacturing method, and examples thereof include a pulverizing method, a suspension polymerization method, an emulsion polymerization method, a solution polymerization method, and an ester elongation polymerization method.
  • carrier ferrite resin coated carrier having a volume average particle size of 40 ⁇ m was used.
  • ferrite non-resin-coated carrier, an iron powder type and a binder type carrier are also usable.
  • the bias voltage applying section 110 applies a bias voltage that has a waveform as shown in FIG. 3 to the development sleeve 9 of the developing roller 3 which is an oscillating bias voltage as an alternating voltage in which a development-side electrical potential that applies a force to move the toner from the developing roller 3 to the photoreceptor 51 and an opposite development-side electrical potential that applies a force to move the toner from the photoreceptor 51 to the developing roller 3 alternate with each other periodically.
  • a bias voltage waveform is repeatedly applied in which a first period where a peak-to-peak voltage (hereinafter, referred to as a Vpp) of a bias voltage is large is provided and a second period where Vpp is small is Provided following the first period.
  • a frequency f 2 of the second period is set to be lower than a frequency f 1 of the first period.
  • t 1 a time during which a development-side potential to move toner from the development sleeve 9 to the photoreceptor 51 is applied.
  • t 2 a time during which an opposite development-side potential to move toner from the photoreceptor 51 to the development sleeve 9 is applied.
  • a large electric field acts on toner in the first period so that the toner is easily separated from carrier and the toner flies from the carrier to the photoreceptor 51 .
  • a flying amount of the toner at this time is substantially the same as in the case of using the waveform in which the same Vpp is applied repeatedly at all times.
  • a state where Vpp( 1 ) is applied is shifted to a state where Vpp( 2 ) which is a small Vpp is applied, and the frequency f 2 of the second period during which Vpp( 2 ) is applied is lower than the frequency f 1 of the first period during which Vpp( 1 ) is applied so that dot reproducibility is improved. This seems to be because the toner flying to the photoreceptor 51 in the first period during which a large Vpp( 1 ) is applied moves gradually to a dot latent image to thereby form stable dots.
  • the potential finally applied In the first period is preferably the development-side potential.
  • the bias waveform as shown in FIG. 4 that is, in the case where the potential finally applied in the first period is the opposite development-side potential, the image density is decreased and dot reproducibility is lowered.
  • the first period during which a large Vpp is applied is completed with the development-side potential finally applied and is directed to the second period in a state where toner is moving to the photoreceptor 51 to reduce Vpp.
  • the toner is easily developed to a latent image and the toner is also gradually developed to a dot latent image at the same time.
  • the period is shifted to the second period in a state where an electric filed is applied in a direction that the toner returns to the development sleeve 9 and Vpp is reduced, thus, it is hard to direct the toner to the photoreceptor 51 and it is hard to reproduce dots. Accordingly, the image density is low and dot reproducibility is lowered.
  • experiment data were obtained by using a multifunctional peripheral MX-7001N manufactured by Sharp Corporation as an image forming apparatus.
  • various developing bias waveforms were output by using an arbitrary waveform generator (trade name: HIOKI 7075, manufactured by HIOKI E. E. CORPORATION) and an amplifier (trade name: HVA4321, manufactured by NF Corporation).
  • the toner used for the experiments has the volume average particle size of 7 micron, which was measured by a commercially available Coulter Counter model TA-II.
  • the image density was obtained by measuring a solid image density by a portable spectrodensintometer (trade name: X-Rite 939, manufactured by X-Rite Incorporated). Dot reproducibility was simply evaluated by printing an isolated dot in which printing was made for one dot and no printing was made for three dots and measuring a density of an area including the isolated dot. Moreover, a density of a non-image area having no printing was measured in the same manner as the case of dot reproducibility to evaluate fog by a difference from a density of a blank sheet not subjected to a printing step. The densitometer used for evaluating dot reproducibility and fog was the same one used for measuring a solid image density.
  • Example 1 was conducted such that Vpp( 1 ) was 1.6 kV, Vpp( 2 ) was 320 V, the frequency f 1 in the first period was 10 kHz, the frequency f 2 in the second period was 3.3 kHz, the periodic number in the first period was twice, and the periodic number in the second period was once.
  • a DC component Vdc of the developing bias was changed into three kinds of ⁇ 300 V, ⁇ 350 V, and ⁇ 400 V to measure the image density of a solid area.
  • a graph of FIG. 5 shows results.
  • the image density (ID) of the solid image is taken along the vertical axis of the graph.
  • Example 1 Comparing Example 1 and Comparative example 1, the image density higher by about 0.3 than that of Comparative example 1 was obtained in Example 1 regardless of DC component Vdc of the developing bias. Moreover, almost the same level of density as the image density in Comparative example 2 was obtained. This seems to be because of the first period during which a large Vpp is applied as described above.
  • the image density of an isolated dot in which printing was made for one dot and no printing was made for three dots was measured.
  • the image density of the isolated dot represents dot reproducibility, and the reproducibility is able to be determined as being excellent as the image density is higher.
  • a graph of FIG. 6 shows results.
  • the image density (ID) of the isolated dot is taken along the vertical axis of the graph.
  • Example 1 Comparing Example 1 and Comparative example 1, the image density higher than that of Comparative example 1 was obtained in Example 1. Moreover, a dot density in Comparative example 2 was very low so that dot reproducibility was hardly obtained. This seems to be because of the second period during which a small Vpp is applied as described above.
  • a difference between a non-image area potential of the photoreceptor 51 and a DC voltage of the developing bias was defined as a cleaning field (hereinafter referred to as a CF) and a difference between the image density of the non-image area and the image density of a blank sheet ( ⁇ ID) in a case where the CF was changed into 150 V, 100 V, and 50 V was measured, respectively.
  • the ⁇ ID represents fog and the fog is able to be determined as being suppressed as the ⁇ ID is smaller.
  • a graph of FIGS. 7 shows results.
  • the image density difference ( ⁇ ID) is taken along the vertical axis of the graph.
  • Example 1 The image density difference of Example 1 is slightly higher than that of Comparative example 2, but almost the same as that of Comparative example 1 regardless of the CF.
  • Example 1 showed that dot reproducibility was improved and toner fog was not deteriorated while increasing the image density.
  • the waveform of the developing bias was fixed to the waveform shown in FIG. 3 and parameters of Vpp( 1 ), Vpp( 2 ), the first frequency f 1 , the second frequency f 2 , the first periodic number, the second periodic number, Vpp( 2 )/Vpp( 1 ), the first period T 1 , the second period T 2 , T 2 /T 1 , and the final potential were changed variously to evaluate the image density, dot reproducibility, and fog in the same manner as the above.
  • the first periodic number represents the number of periods included in the first period and the second periodic number represents the number of periods included in the second period.
  • the case where the final potential was the development-side potential was shown as “Positive” and the case of the opposite development-side potential was shown as “Opposite”.
  • Table 1 shows comprehensive results compared to the result of Comparative example 1.
  • the exceeding result was represented by “Good”, the equivalent result was represented by “Not bad”, and the lower result was represented by “Poor”.
  • the image density compared to the image density in a case where DC bias was 50 V higher than the above-described condition, the exceeding result was represented by “Good”, the equivalent result was represented by “Not bad”, and the lower result was represented by “Poor”.
  • the first periodic number was preferably twice or three times.
  • the first periodic number was once like in Conditions 8 and 9 a capability of returning toner from the photoreceptor 51 to the development sleeve 9 was insufficient, thus making it impossible to prevent deterioration of fog.
  • the first periodic number was four times like in Condition 19 the capability of returning toner from the photoreceptor 51 to the development sleeve 9 was so strong adversely that dot reproducibility was deteriorated.
  • the first periodic number was preferably twice or three times, and most preferably twice.
  • the second periodic number was preferably once.
  • the second periodic number was twice like in Condition 17 a time for moving toner from the development sleeve 9 to the photoreceptor 51 gradually lacks, thus making it impossible to prevent that dot reproducibility is lowered As a result, the second periodic number was preferably once or more.
  • Vpp( 2 )/Vpp( 1 ) was preferably 0.1 to 0.3, and more preferably 0.15 to 0.25.
  • T 2 /T 1 was preferably 0.7 to 2.5, and more preferably 1.0 to 2.0.
  • Vpp( 1 ) was preferably 3 kV or less.
  • Vpp( 1 ) was lower than 1 kV like in Condition 21, the image density was insufficient and there was no merit to utilize the invention.
  • the image density was further increased when Vpp( 1 ) was increased, however, when being 3 kV like in Condition 22, a leak is generated between the photoreceptor and the development sleeve so that a spot-like white void was easily generated. Therefore, upper limit of Vpp( 1 ) was 3 kV.
  • the waveform of the developing bias voltage in this embodiment is different from the first embodiment.
  • the bias voltage applying section 110 applies a bias voltage of the waveform as shown in FIG. 8 to the development sleeve 9 of the developing roller 3 as an oscillating bias voltage which is an alternating voltage in which a development-side potential that applies a force to move toner from the developing roller 3 to the photoreceptor 51 and an opposite development-side potential that applies a force to move toner from the photoreceptor 51 to the developing roller 3 alternate with each other periodically.
  • t 1 a time during which the development-side potential that moves toner from the development sleeve 9 to the photoreceptor 51 is applied during one period
  • t 2 a time during which the opposite development-side potential that moves toner from the photoreceptor 51 to the development sleeve 9 is applied as t 2 in the first period during which Vpp( 1 ) is applied
  • a suitable range of t 1 /(t 1 +t 2 ) ⁇ 100(%) is preferably 35 to 70%, and more preferably 40 to 65%.
  • a time during which the development-side potential that moves toner from the development sleeve 9 to the photoreceptor 51 is applied during one period and a time during which the opposite development-side potential that moves toner from the photoreceptor 51 to the development sleeve 9 is applied are the same, but may be different similarly to the first period.
  • Vpp( 1 ) was 1.6 kV
  • Vpp( 2 ) was 480 V
  • the frequency f 1 of the first period was 10 kHz
  • the frequency f 2 of the second period was 3.3 kHz
  • the periodic number of the first period was twice
  • the periodic number of the second period was once
  • t 1 /(t 1 t 2 ) ⁇ 100 60% in the first period
  • which is a difference between a voltage to be applied during t 1 and an average voltage
  • which is a difference between a voltage to be applied during t 2 and an average voltage was 960 V.
  • the following Table 2 shows the example 3 as Condition 24.
  • the waveform of the developing bias was fixed to the waveform shown in FIG. 8 and parameters of
  • ⁇ t 1
  • ⁇ t 2 and Vpp
  • Table 2 shows comprehensive results compared to the result of Comparative example 1. Compared to Comparative example 1, the exceeding result was represented by “Good”, the equivalent result was represented by “Not bad”, and the lower result was represented by “Poor”. In addition, the result exceeding Condition 4 in the first embodiment was represented by “Excellent”.
  • Vpp(1) Vpp(2) f1 f2 periodic periodic Image Dot Conditions [V] [V] [kHz] [kHz] number number
  • Fog Condition 4 1600 320 10 3.3 2 1 800 800 50% Good Good Good Condition 24 1600 320 10 3.3 2 1 640 960 60% Good Good Excellent Condition 25 1600 320 10 3.3 2 1 560 1040 65% Good Good Excellent Condition 26 1600 320 10 3.3 2 1 480 1120 70% Not bad Not bad Excellent Condition 27 1600 320 10 3.3 2 1 320 1280 80% Poor Not bad Excellent Condition 28 1600 320 10 3.3 2 1 960 640 40% Good Excellent Good Condition 29 1600 320 10 3.3 2 1 1040 560 35% Good Excellent Not bad Condition 30 1600 320 10 3.3 2 1 1120 480 30% Good Excellent Poor Poor
  • t 1 /(t 1 +t 2 ) ⁇ 100(%) is preferably 35 to 70%, and more preferably 40 to 65%.
  • the invention relates to a developing bias that moves toner, and the similar effect is also obtained in one-component developer without limitation to two-component development. Moreover, the similar effect is also obtained in a contact developing method in which development is performed with developer being in contact with the photoreceptor and a non-contact developing method in which development is performed with developer being not contact with the photoreceptor.

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  • Developing For Electrophotography (AREA)
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  • Color Electrophotography (AREA)
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US20110243592A1 (en) * 2010-03-31 2011-10-06 Canon Kabushiki Kaisha Electrophotographic image forming apparatus using a periodic wave as a developing bias
US20120070178A1 (en) * 2010-09-17 2012-03-22 Canon Kabushiki Kaisha Power supply circuit for supplying power to electronic device such as image forming apparatus
US8761629B2 (en) 2010-09-22 2014-06-24 Canon Kabushiki Kaisha Power supply circuit for supplying power to electronic device such as image forming apparatus

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JP2008145959A (ja) * 2006-12-13 2008-06-26 Sharp Corp 現像方法及び画像形成装置
JP4734358B2 (ja) * 2008-02-27 2011-07-27 シャープ株式会社 現像装置および画像形成装置
JP5539057B2 (ja) * 2010-06-21 2014-07-02 キヤノン株式会社 画像形成装置
JP5399337B2 (ja) * 2010-07-23 2014-01-29 京セラドキュメントソリューションズ株式会社 現像装置およびそれを備えた画像形成装置
JP6125896B2 (ja) 2013-05-14 2017-05-10 富士フイルム株式会社 皮膚洗浄料

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US8761629B2 (en) 2010-09-22 2014-06-24 Canon Kabushiki Kaisha Power supply circuit for supplying power to electronic device such as image forming apparatus

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